Liquid crystal display device

ABSTRACT

To reduce an optical leakage and a disclination.  
     In a liquid crystal display device for a gate line inversion drive, of the end portion of a pixel electrode, the portions formed along a scanning line are raised with respect to the main face of the pixel electrode. Of the end portions of a pixel electrode, the portions formed along a signal line are formed to have a height identical to that of the main face of the pixel electrode.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device includinga circuit composed of field effect transistors (FET) such as thin filmtransistors (TFT), and to a method for manufacturing the semiconductordevice. The TFT means a semiconductor element including a semiconductorlayer, a gate electrode, a source electrode and a drain electrode.

[0003] Here, the “element substrate” generally indicates the substratehaving a semiconductor element such as the TFT.

[0004] Here, the “display device”) generally indicates the device fordisplaying the brightness with the change in an electric signal, and thedisplay device for displaying by applying the electric signal to aliquid crystal.

[0005] 2. Related Art

[0006] In recent years, there has been noted a technique forconstructing the TFT by using a semiconductor thin film (having athickness of about several to several hundreds nm) formed over asubstrate having an insulating surface. The TFT is widely applied to anelectronic device such as an IC or a semiconductor device and isurgently demanded for a development as the switching element of theliquid crystal display device.

[0007] This liquid crystal display device is coarsely divided into twoknown kinds: the active matrix type and the passive matrix type. Theliquid crystal display device of the active matrix type uses the TFT asthe switching element and can achieve an image of a high quality. Thegeneral application of the active matrix type is a note-type personalcomputer but is expected as a home TV set or a mobile terminal.

[0008] Of the liquid crystal display device of the active matrix type, aliquid crystal display device of a projection type is enabled to achievea large screen display by enlarging the frame to a screen. In theprojection type liquid crystal display device of recent years, there hasbeen developed the technique for making the liquid crystal displaydevice mobile by reducing the size of the liquid crystal panel to reducethe size of the optical system. With this size reduction in the opticalsystem, the cost for the optical system can be lowered to provide theliquid crystal display device at a reasonable cost.

[0009] Here, it is customary to subject the active matrix type liquidcrystal display device to line inversion drives. Of these line inversiondrives, the source line inversion drive is made such that the polaritiesof signal voltages to be written in pixel TFTs connected with m-columnsof signal lines are different between the adjoining signal lines, asshown in a top plan view of the pixel portion of FIG. 30. For odd frames(FIG. 30A) and even frames (FIG. 30B), moreover, there are changed thepolarities of the signal voltages to be written in the pixel TFTsconnected with signal lines. The liquid crystals are prevented fromburning by changing the polarities of the signal voltages to be writtenin the pixel TFTs thereby to drive the liquid crystal with an ACcurrent. The gate line inversion drive may be effected by replacing thesignal lines of FIG. 30 by scanning lines.

[0010] An object of the present invention is to provide an active matrixtype liquid crystal display device and an element structure which isenabled to prevent an optical leakage and a disclination by examiningthe principle of the disclination and the optical leakage of a liquidcrystal systematically.

[0011] In the interface of an alignment film, the liquid crystal isoriented to raise its one end. The “pre-tilt direction” will be termedas the positive projection of the direction, as extended from one end ofthe liquid crystal molecule the closest to the interface of thealignment film to the other end raised from the alignment film, upon thesubstrate face. Moreover, the “pre-tilt angle” will be termed as theangle made between the interface of the alignment film and the longeraxis of the liquid crystal near the interface of the alignment film. Thepre-tilt angle is given by a rubbing treatment or by applying anelectric field to the liquid crystal to switch the liquid crystal nearthe interface of the alignment film.

[0012] Moreover, the orientation failure, as caused by the fact that thedirection of the pre-tilt of the near liquid crystal is generallyopposed in the alignment film interface, will be called the“disclination”. On the other hand, there is a region where the pre-tiltangle is locally different due to the electric field distribution or theheterogeneous rubbing although the pre-tilt direction of the liquidcrystal is identical. The orientation failure, as thus caused when theorientation state is not normal, is that the brightness is locally sohigh when two polarization plates are arranged on the liquid crystalpanel that the light looks as if it leaks. Therefore, the orientation ofthe liquid crystal, in which the direction of the pre-tilt is identicalbut the pre-tilt angle is locally different, will be called the “opticalleakage”.

[0013] When the liquid crystal display device is driven by the activematrix type, the display quality is degraded by the optical leakage andthe disclination. In other words, in the normally white mode, ashielding film is required for shielding the optical leakage and thedisclination so that the aperture ratio decreases.

[0014] In the liquid crystal display device having fine pixels as in theprojection type liquid crystal display device, the disclination and theoptical leakages, if any, will take an innegligible ratio in the pixels.If the optical leakage and the disclination cannot be shielded due tothe misalignment of the shielding film, moreover, they are visuallyrecognized like bright lines, when displayed in black, to lower thecontrast. In short, it is important for the projection type liquidcrystal display device how the optical leakage and the disclination areto be suppressed.

[0015] As compared with the smectic liquid crystal having a layerstructure and accordingly a high orientation order, the nematic liquidcrystal is easily subjected to the disclination and the optical leakageby the electric field established between pixel electrodes. Especiallyin the orientation system using the nematic liquid crystal, therefore,countermeasures are required for reducing the disclination and theoptical leakage.

[0016] The reason why the optical leakage and the disclination occurwill be described with reference to a schematic diagram presenting asection of the pixel portion of a liquid crystal display device of FIG.12. In the adjoining pixel electrodes of FIG. 12, it is assumed that apixel electrode 101 a has a potential of +5 V whereas a pixel electrode101 b has a potential of −5 V. An opposed electrode 102 is assumed tohave a potential of 0 V. In a region where equipotential lines 103 areformed in parallel with the surfaces of the pixel electrodes, thepositive type liquid crystals are arranged such that their molecules 108are normal at their longer axes to the surfaces of the pixel electrodes.At the ends of the pixel electrodes, however, the equipotential linescurve so that liquid crystal molecules 106 are oriented obliquely withrespect to the surfaces of the pixel electrodes to cause the orientationfailure. It is considered important for reducing the orientation failurehow much the curvatures of the equipotential lines at the ends of thepixel electrodes are reduced.

[0017] At the ends of the pixel electrodes, there are formed regions 104of the optical leakage in which the pre-tilt angle is locally different.This is because the equipotential lines curve at the end portions of thepixel electrodes so that the liquid crystal molecules 106 cannot be soswitched at the end portions of the pixel electrodes as to have theirlonger axes normal to the surfaces of the pixel electrodes.

[0018] Moreover, there is formed a region where the pre-tilt directionof the liquid crystals is reversed by the electric field at the ends ofthe pixel electrodes from the pre-tilt direction determined by a rubbingdirection 107. Then, the pre-tilt angle and the pre-tilt direction ofthe alignment film interface are locally abruptly changed to enlarge theorientation strain of the liquid crystals thereby to form regions 105where the disclination occurs.

[0019] It is understood that the disclination and the optical leakageare caused from one reason that the equipotential lines parallel to thesurfaces of the pixel electrodes curve at the end portions of the pixelelectrodes. The present invention to be described in the following is sostructurally devised that the curvatures of the equipotential lines aresuppressed as much as possible and that the equipotential lines curve,if so, as close to the ends of the pixel electrodes as possible.

SUMMARY OF THE INVENTION

[0020] In order to solve the problems thus far described, there havebeen adopted the following means. The end portions of the pixelelectrodes are classified into band-shaped first, second, third andfourth end portions. In the pixel electrode, moreover, the flat face, asenclosed by the first end portion, the second end portion, the third endportion and the fourth end portion, will be called the “main face” ofthe pixel electrode. Here, the end portion of the pixel electrodeincludes the ends of the pixel electrode, i.e., the portions extendingin a band shape by several μm from the ends of the pixel electrode. Themain face of the pixel electrode is a flat face occupying 20% or more,preferably 50% or more of the area of the pixel electrode. In short, theflat face occupying the maximum area of the pixel electrode is the mainface of the pixel electrode.

[0021] One example of the pixel of the present invention will bedescribed with reference to the top plan view of the pixel portion ofthe liquid crystal display device of FIG. 2. Of the end portions of afirst pixel electrode 208 of the liquid crystal display device for thegate line inversion drive, a first end portion 201 of the pixelelectrode is extended along a first scanning line 207A. A third endportion 203 opposed to the first end portion 201 of the first pixelelectrode is extended along a second scanning line 207B adjoining thefirst scanning line. A second end portion 202 is extended along a firstsignal line 212A. A fourth end portion 204 is extended along a secondsignal line 212B. The second signal line 212B is adjacent to the firstsignal line 212A. The two end portions 206A and 206B of the first endportion are extended at their one side along the first signal line 212Aand the second signal line 212B, respectively. The two end portions 205Aand 205B of the third end portion are extended at their one side alongthe first signal line 212A and the second signal line 212B,respectively.

[0022] The pixel electrodes adjoining first end portion 201 and thethird end portion 203 are at the potential of polarity different fromthat of the first end portion and the third end portion. The pixelelectrodes adjoining second end portion 202 and the fourth end portion204 are at the potential of polarity identical to that of the first endportion and the third end portion. With reference to FIG. 2, in theliquid crystal display device for the gate line inversion drive, thereis a second pixel electrode 209 which adjoins the first pixel electrode208 across the first scanning line 207A. Then, there adjoin the firstend portion 201 of the first pixel electrode 208 and the third endportion 203 of the second pixel electrode 209. At the pixel electrodesadjoining each other across the scanning line, between the first endportion of the first pixel electrode and the third end portion of thesecond pixel electrode, there is established an electric field as aresult that the pixel electrodes having the potentials of differentpolarities adjoin each other.

[0023] In the liquid crystal display device for the source lineinversion drive, it is sufficient to replace the first scanning line207A of FIG. 2 by the first signal line and the second scanning line207B by the second signal line. It is naturally necessary to replace thefirst signal line 212A by the first scanning line and the second signalline 212B by the second scanning line. In other words, the liquidcrystal display device for the source line inversion drive, too, it isnot different from the liquid crystal display device for the gate lineinversion drive that the electric field is established between the firstend portion of the first pixel electrode and the third end portion ofthe second pixel electrode as a result that the pixel electrodes ofdifferent polarities adjoin each other.

[0024] It can be thought that the optical leakage and the disclinationcan be reduced by suppressing the curvatures of the equipotential linesto be formed at the ends of the pixel electrodes. However, the degree ofcurvatures of the equipotential lines at the pixel electrode endportions changes depending upon whether the adjoining pixel electrodesare at identical or different polarities. Considering whether theadjoining pixel electrodes are at identical or different polarities,therefore, the countermeasures have been made for the following cases(1) and (2) by predicting it necessary to propose a structure forsuppressing the curvatures of the equipotential lines.

Ridges of Pixel Electrode End Portions

[0025] (1) Adjoining Pixel Electrodes at Different Polarities

[0026] It has been simulated how the orientation of the liquid crystalis changed by disposing the first end portion and the third end portionof the pixel electrode at a level close to the opposed electrode withrespect to the main face of the pixel electrode. This simulation modelis shown in FIG. 3. The simulation model of FIG. 3 presents a section ofthe pixel portion of the liquid crystal display device. The cell gap (d)indicates the distance from the surface of the opposed electrode to themain face of the pixel electrode. The distance (s) between the pixelelectrodes indicates the distance, which is measured for the pixelelectrodes adjoining in the direction parallel to the row direction ofthe display region from the end point of the pixel electrode to the endof the adjoining pixel electrode in the drawing, as formed by projectingthe shape of the adjoining pixel electrodes positively on a planecontacting with the main face of the pixel electrode. For the pixelelectrodes adjoining in the column direction, the distance is measuredin the direction parallel to the column direction of the display regionfrom the end point of the pixel electrode to the end point of theadjoining pixel electrode. The distance between the pixel electrodes maybe locally different but is represented by the distance sharing themaximum ratio in the distribution of the distances between the pixelelectrodes. If the liquid crystal display device for the gate lineinversion drive is assumed, the distance between the pixel electrodes inthe present simulation is the distance (s) between the first pixelelectrode 208 and the second pixel electrode 209 in the top plan view ofFIG. 2.

[0027] In FIG. 3, the individual electrodes have the followingpotentials: a first pixel electrode 303 a at +5 V; a second pixelelectrode 303 b at −5 V; and an opposed electrode 301 at 0V. A liquidcrystal 302 is exemplified by ZLI4792 made by MERK Company, and has apre-tilt angle of 6.0 degrees, a sinistrous chiral pitch of 70 μm and atwist angle of 90 degrees. The pixel pitch (p) is 18 μm. The distance(s) between the first pixel electrode and the second pixel electrode is2.0 μm. The cell gap (d) is 4.5 μm. It is assumed that the pixelelectrode and the opposed electrode are formed over a transparentsubstrate 307. The structure is made by repeating the units of thesimulation model of FIG. 3 periodically. In FIG. 3, there are shownrubbing directions 305 and 306. The simulation software used was LCDMaster of SHINTEC Company.

[0028] Moreover, the simulation was done by using the presence andabsence of a ridge 304 and the width (L₁) of the first end portion asparameters. The first end portion and the third end portion are formedto rise from the flat face. The overlapping widths between the ridge andthe pixel electrode, i.e., the width (L₁) of the first end portion andthe width (L₂) of the third end portion are the shortest length fromeach point of the end of the pixel electrode to the side opposed to thatpoint, in a polygon which is formed by projecting the portions raisedfrom the main face of the pixel electrode, positively on the face tocontact with the main face of the pixel electrode. Here in theconstruction having the end portions of the pixel electrode on theridge, the height of the first end portion is the distance between theface to contact with the main face of the pixel electrode and theuppermost end portion of the first end portion. The height of the thirdend portion is the distance between the face to contact with the mainface of the pixel electrode and the uppermost end portion of the thirdend portion. The heights (h) of the first end portion and the third endportion are set to 0.5 μm in the simulation. In this simulation, thewidth (L₁) of the first end portion and the width (L₂) of the third endportion are equalized. Moreover, the heights (h) of the first endportion and the third end portion are also equalized.

[0029] Under the conditions of the simulations, there adjoin the firstpixel electrode 303 a and the second pixel electrode 303 b which havepotentials of polarities different from each other. In the liquidcrystal display device for the gate line inversion drive, specifically,the model of FIG. 3 indicates that the first pixel electrode 303 a andthe second pixel electrode 303 b adjoining the former in the columndirection have the potentials of polarities different from each other,and that a first end portion 1001 of the first pixel electrode and athird end portion 1002 of the second pixel electrode adjoin each other.

[0030] In the liquid crystal display device for the source lineinversion drive, specifically, the model indicates that the first pixelelectrode 303 a and the second pixel electrode 303 b adjoining theformer in the row direction have the potentials of polarities differentfrom each other, and that the first end portion 1001 of the first pixelelectrode and the third end portion 1002 of the second pixel electrodeadjoin each other.

[0031] The results of the representative simulations presenting thecharacteristics are shown in FIG. 13 and FIG. 14. FIG. 13 and FIG. 14present relations between the width and transmittance of the pixelelectrode overlapping the ridge. FIG. 13A shows the case in which thepixel electrode is formed on the flat face; FIG. 13B shows the case inwhich the ends (i.e., the first end portion and the third end portion)of the pixel electrode are formed over the ridge by 1.4 μm; and FIG. 14shows the case in which the ends (i.e., the first end portion and thethird end portion) of the pixel electrode are formed over the ridge by4.0 μm. It is indicated that the better black display is realized forthe lower transmittance. The results of the simulation show the pixelelectrode, the opposed electrode, and the director of the liquidcrystal, the equipotential lines and the transmittance. In the actualsimulation, the pixel electrode is disposed at the portion of a scale of1 μm to 16 μm of the abscissa, and the pixel electrode is disposed atthe portion of a scale of 19 μm to 35 μm of the abscissa. Moreover, thepixel electrodes adjoin each other at a gap of 2 μm. Because thedisclination and the optical leakage at the portions of the ends of thepixel electrode are noted, however, the portion of the scale of 10 μm to26 μm of the abscissa is shown in an enlarged scale in FIG. 13 and FIG.14. If the pixel electrode is on the flat face, as shown in FIG. 13A,the equipotential lines curve at the end portions of the pixelelectrode. When the first end portion of the first pixel electrode andthe third end portion of the second pixel electrode are disposed at aheight as high as the opposed electrode, as compared with the main faceof the pixel electrode, as shown in FIG. 13B, however, the equipotentiallines are formed along the surface of the pixel electrodes in thevicinity of the first end portion of the first pixel electrode and thethird end portion of the second pixel electrode. Therefore, thecurvatures of the equipotential lines in the vicinity of the first endportion of the first pixel electrode and the third end portion of thesecond pixel electrode are slightly suppressed to reductions in thedisclination and the optical leakage. If the widths of the first endportion and the third end portion are enlarged, as shown in FIG. 14,however, even the equipotential lines having been intrinsically parallelto the flat face having the first pixel electrode and the third pixelelectrode are curved toward the opposed electrode due to the first endportion and the third end portion, as raised with respect to the mainface of the pixel electrode, so that the disclination and the opticalleakage increase. In short, it has been understood that when theadjoining pixel electrode have the potentials of the differentpolarities, the first end portion of the first pixel electrode and thethird end portion of the second pixel electrode are preferably raisedfrom the main face of the pixel electrode and disposed at a high as theopposed electrode, but that the width of the first end portion and thewidth of the third end portion have the optimum values for reducing theoptical leakage and the disclination.

[0032] The results of FIG. 13 and FIG. 14 will be summarized withspecific numeral values. The sum of the widths of the optical leakageand the disclination is designated by x (μm).

[0033] When the pixel electrodes are on the flat face, as shown in FIG.13A, x=9.2 μm;

[0034] When the first end portion of the first pixel electrode has awidth of 1.4 μm and when the third end portion of the second pixelelectrode has a width of 1.4 μm, as shown in FIG. 13B, x=6.8 82 m; and

[0035] When the first end portion of the first pixel electrode has awidth of 4.0 μm, and when the third end portion of the second pixelelectrode has a width of 4.0 μm, as shown in FIG. 14, x=9.3 μm.

[0036] By comparing these three simulation results, the effect tosuppress the optical leakage and the disclination is high when the firstend portion and the third end portion have the width of 1.4 μm.

[0037] The results of simulations as made by changing the relationsbetween the width (L₁) of the first end portion and the sum (x) of thewidths of the optical leakage and the disclination for the cell gap (d),the height (h) of the first end portion, the distance (s) between thefirst pixel electrode and the second pixel electrode and the pitch (p)of the pixels, are shown in FIG. 11. In FIG. 11, the abscissa indicatesthe overlap width (i.e., the width of the first end portion) of thepixel electrode and the ridge, and the ordinate indicates the sum of thewidths of the optical leakage and the disclination. It is indicated thatthe quality of the black display is the better for the less sum of thewidths of the optical leakage and the disclination. The simulations aremade with the height of the first end portion 1001 and the height of thethird end portion 1002 being equal. It is indicated that if the heightof the first end portion is 0.5 μm, the height of the third end portionis necessarily 0.5 μm. In the simulations, moreover, the width (L₁) ofthe first end portion and the width (L₂) of the second pixel electrodeare equalized. It is, therefore, indicated that if the width of thefirst end portion is 0.5 μm, the width of the third end portion isnecessarily 0.5 μm.

[0038] If the heights of the first end portion and the third end portionare small, the effect to suppress the disclination and the opticalleakage tends to be low, and it is, therefore, preferable that theheights of the first end portion and the third end portion are 0.5 μm ormore. When the heights of the first end portion and the third endportion are 0.5 μm or more, the cell gap is 4.5 μm or less. It is alsounderstood that the sum of the widths of the optical leakage and thedisclination becomes more than that without the first end portion andthe third end portion for the distance of 4.0 μm or less between thepixel electrodes, unless the width of the first end portion and thewidth of the third end portion are suppressed within 3.0 μm from theends of the pixel electrode.

[0039] By comparing FIG. 11A and FIG. 11B, it is understood that theeffect obtained by raising the first end portion and the third endportion with respect to the main face of the pixel electrode to theheight nearly that of the opposed electrode appears the more prominentespecially as the cell gap becomes the larger. If the cell gap is large,the electric field to be established between the opposed electrode andthe pixel electrode is weak so that the equipotential lines are liableto curve at the end portions of the pixel electrode. Thus, it isunderstood that when the curvatures of the equipotential lines are largeat the end portions of the pixel electrode, the curvatures of theequipotential lines are effectively suppressed by raising the first endportion and the third end portion with respect to the main face of thepixel electrode.

[0040] Moreover, the simulations are further made by changing the pixelpitch (p). For the pixel of a pitch of 18 μm and the pixel of a pitch of43 μm, however, the degrees of the optical leakage and the disclinationare not largely changed. This is because the disclination and theoptical leakage are the phenomenon to occur at the end portions of thepixel electrode (FIG. 11A).

[0041] (2) Adjoining Pixel Electrodes at Identical Polarities

[0042] In the liquid crystal display device of the gate line inversiondrive in a top plan view of a pixel portion in FIG. 2, of the endportions of the pixel electrode, the fourth end portion 204 of the firstpixel electrode 208 adjoins the second end portion 202 of a third pixelelectrode 210, as having the potential of the identical polarity.Therefore, here will be detailed how to make the structures of thesecond end portion and the fourth end portion having the potentials ofthe identical polarity and adjoining each other.

[0043] This description will be described with reference to FIG. 2. Inthe liquid crystal display device for the gate line inversion drive,when the pixel electrodes adjoining across the signal line 212B are atthe potentials of the identical polarity, the changes in the orientationof the liquid crystal are compared between the cases, in which for thesecond end portion 202 of the third pixel electrode 210 and the fourthend portion 204 of the first pixel electrode 208, the second end portionand the fourth end portion are raised with respect to the main face ofthe pixel electrode so that they are formed to the same level nearlythat of the opposed electrode and to the flat face.

[0044] In the simulation model of FIG. 3, it is assumed that the pixelelectrode adjoining the first end portion 303 a is the third pixelelectrode 303 b. It is also assumed that the width (L₁) of the secondend portion and the width (L₂) of the fourth end portion are equalized.

[0045] The simulation conditions are identical to those of (1) “theridges of the pixel electrode end portions” excepting that both thefirst pixel electrode 303 a and the third pixel electrode 303 b have thepotential of +5 V. Specifically, the potential of the opposed electrodeis 0 V, and the distance (s) between the first pixel electrode 303 a andthe third pixel electrode 303 b is 2.0 μm. The height (h) of the secondend portion and the height (h) of the fourth end portion are 0.5 μm. Thecell gap (d) is 4.5 μm. The physical properties of the liquid crystal ofthe simulation use the data of ZLI4792 at the room temperature. Thepre-tilt angle and the twist angle of the liquid crystal are 6 degreesand 90 degrees, and the rubbing directions are indicated by 305 and 306.

[0046] The results of the simulation are shown in FIGS. 15 and 16. FIGS.15 and 16 show the changes in the transmittance against the overlapwidth of the pixel electrode and the ridge when the pixel electrodeshaving the potentials of the identical polarity adjoin each other. It isindicated that the more excellent black display is made for the lowertransmittance. FIG. 15A shows the case in which the pixel electrodes areformed on the flat face; FIG. 15B shows the case in which the ends(i.e., the first end portion and the third end portion) of the pixelelectrode are formed over the ridge by 1.4 μm; and FIG. 16 shows thecase in which the ends (i.e., the first end portion and the third endportion) of the pixel electrode are formed over the ridge by 4.0 μm. Inthe actual simulation, the pixel electrode is disposed at the portion ofa scale of 1 μm to 16 μm of the abscissa, and the pixel electrode isdisposed at the portion of a scale of 19 μm to 35 μm of the abscissa.Moreover, the pixel electrodes adjoin each other at a gap of 2 μm.Because the disclination and the optical leakage at the portions of theends of the pixel electrode are noted, however, the portion of the scaleof 10 μm to 26 μm of the abscissa is shown in an enlarged scale in FIG.15 and FIG. 16. The results of FIG. 15 and FIG. 16 will be summarizedwith specific numeral values. The magnitude of the optical leakage isindicated by the maximum (%) of the transmittance. Here is not thedisclination which might otherwise be caused by reversing the pre-tiltdirection at the interface of the alignment film.

[0047] When the pixel electrodes are on the flat face, as shown in FIG.15A, the transmittance of the optical leakage has a maximum of 0.3%;

[0048] When the second end portion of the first pixel electrode has awidth of 1.4 μm and when the fourth end portion of the third pixelelectrode has a width of 1.4 μ, as shown in FIG. 15B the transmittanceof the optical leakage has a maximum of 1.0%; and

[0049] When the second end portion of the first pixel electrode has awidth of 4.0 μm and when the fourth end portion of the third pixelelectrode has a width of 4.0 μm, as shown in FIG. 16 the transmittanceof the optical leakage has a maximum of 1.0%.

[0050] When the adjoining pixel electrodes are at the potentials of theidentical polarity, the equipotential lines are formed generally inparallel with the flat face in which the pixel electrodes are formed. Itis in the region between the pixel electrodes where the equipotentiallines curve. Without the ridge below the second end portion and thefourth end portion of the pixel electrode, therefore, the opticalleakage is little, if any (FIG. 15A). Moreover, when the second endportion and the fourth end portion of the pixel electrode are raisedwith respect to the main face of the pixel electrode to the heightnearly that of the opposed electrode, the equipotential lines, asintrinsically parallel to the flat face having the pixel electrode, arecurved by the ridge so that the optical leakage occurs at the portionscorresponding to the two ends of the ridge (FIG. 15B). As the second endportion and the fourth end portion become the wider so that the two endsof the ridge become the closer to the inside of the pixel electrode, theoptical leakages at the two ends of the ridge occur on the inner side ofthe pixel electrode so that the shielding film for shielding the opticalleakage is required to have the larger width (FIG. 16). When the pixelelectrodes adjoining each other are at the potentials of the identicalpolarity, therefore, it has been understood that the better liquidcrystal orientation can be obtained if the second end portion and thefourth end portion of the pixel electrode are at the same height as thatof the main face of the pixel electrode. In other words, a slightoptical leakage occurs at the second end portion and the fourth endportion of the pixel electrode, too, when the adjoining pixel electrodesare at the identical polarity. However, it is predicted that thecountermeasure of raising the end portions of the pixel electroderesults in adverse effects.

[0051] The simulation of FIGS. 17 and 18 corresponds to the case inwhich the pixel electrodes having the equal potentials adjoin eachother, and examines the changes in the transmittance by changing thedistance between the pixel electrodes. The tendencies are examined bychanging the distance between the pixel electrodes to 2.0 μm, 4.0 μm and6.0 μm.

[0052] From the simulation of FIG. 17 and FIG. 18, it is understood thatthe curvatures of the equipotential lines are the less for the shorterdistance between the first pixel electrode and the third pixel electrodewhen the pixel electrodes adjoin each other at the equal potential. FIG.17 and FIG. 18 show the orientation of the liquid crystal when the firstpixel electrode and the third pixel electrode adjoining are at +5 V ofthe identical polarity and when the opposed electrode is at 0 V. Theliquid crystal used is ZLI4792. The pixel electrodes are formed on theflat face. FIG. 17A shows the orientation of the liquid crystal at thetime when the distance between the pixel electrodes is 2.0 μm. FIG. 17Bshows the orientation of the liquid crystal at the time when thedistance between the pixel electrodes is 4.0 μm. FIG. 18 shows theorientation of the liquid crystal at the time when the distance betweenthe pixel electrodes is 6.0 μm.

[0053] If the distance between the adjoining pixel electrodes of theidentical polarity is 2.0 μm or less, as shown in FIG. 17 and FIG. 18,it is understood that the curvatures of the equipotential lines are notso large. When the distance between the pixel electrodes is 2.0 μm orless, therefore, it is predicted that the formation of the second endportion and the fourth end portion of the pixel electrode rising withrespect to the main face of the pixel electrode is adversely effectivefor the orientation of the liquid crystal. If the second end portion ofthe pixel electrode and the fourth end portion of the pixel electrodeare at the same height as that of the main face of the pixel electrode,the equipotential lines can be made more parallel to the face having thepixel electrodes to improve the orientation of the liquid crystalbetter.

Construction 1 of Pixel Portion of Invention

[0054] On the basis of the analyses thus far made, the features of thepresent invention will be described with reference to FIGS. 1 and 2 andFIG. 4. FIG. 1A shows a top plan view of the pixel electrode, and FIG.1B shows a perspective view of the pixel electrodes arranged in a matrixshape. The top plan view of FIG. 2 shows the positional relationsbetween the signal lines and the scanning lines and the first to fourthend portions of the pixel electrodes when the pixel electrodes shown inFIG. 1A are arranged in the 2×2 matrix. The sections, as taken along thechain lines A-A′ and B-B′ from FIG. 2, are presented in FIGS. 4A and 4B.The chain lines A-A′ and B-B′, as presented in the perspective view ofthe pixel electrode of FIG. 1B, correspond to the top plan view of FIG.2 and the sectional view of FIG. 4.

[0055] The characteristics of the pixel portion of the present inventionwill be described with reference to FIG. 2. The pixel electrode includesthe first end portion 201, the second end portion 202, the third endportion 203 and the fourth end portion 204, and its main facesurrounding by those end portions, and the main face is formed over theflat face. Moreover, the pixel electrode further includes the opposedelectrode opposed to the pixel electrode. The first end portion isextended along the first scanning line 207A; the third end portion isextended along the second scanning line 207B adjoining the firstscanning line 207A; the second end portion is extended along the firstsignal line 212A; and the fourth end portion is extended along thesecond signal line 212B adjoining the first signal line 212A. The twoend portions 206A and 206B of the first end portion 201 are extendedalong the first signal line 212A and the second signal line 212B. Thetwo end portions 205A and 205B of the third end portion 203 are extendedalong the first signal line 212A and the second signal line 212B.Moreover, the first end portion and the third end portion are formed tohave a height nearly that of the opposed electrode with respect to theflat face, and the second end portion and the fourth end portion areformed to have a height nearly that of the flat face. The presentinvention can be applied to the liquid crystal display device for thegate line inversion drive.

[0056] Moreover, the liquid crystal display device for the gate lineinversion drive is characterized in that the pixel electrode includesthe first pixel electrode 208 and the second pixel electrode 209adjoining the first pixel electrode in the column direction, and in thatthe first end portion 201 of the first pixel electrode 208 and the thirdend portion 203 of the second pixel electrode adjoin each other. Thiswill be described with reference to the perspective view of FIG. 1B.Over a scanning line 213, there are the first end portion in the firstpixel electrode 208 and the third end portion in the second pixelelectrode 209. The second end portion and the fourth end portion in thefirst pixel electrode to the fourth pixel electrode are at the sameheight as that of the main face of the pixel electrodes.

[0057] Specifically, for the gate line inversion drive, the first pixelelectrode 208 and the second pixel electrode 209, as opposed to eachother across the first scanning line 207A, as shown in FIG. 2, have thepotentials of polarities different from each other. By forming the firstend portion 201 in the first pixel electrode 208 and the third endportion in the second pixel electrode at a height nearly that of theopposed electrode, the curvatures of the equipotential lines aresuppressed at the first end portion 201 in the first pixel electrode 208and at the third end portion 203 in the second pixel electrode 209thereby to reduce the disclination and the optical leakage effectively(as referred to (1) “the ridges of the pixel electrode end portions”).The second end portion 202 in the first pixel electrode 208 and thefourth end portion 204 in the first pixel electrode are formed on theflat face. The fourth end portion 204 in the first pixel electrode 208and the second end portion 202 in the third pixel electrode 210 have thepotentials of the identical polarity and adjoin each other. It is, themore effective for suppressing the unnecessary curvatures of theequipotential lines and accordingly the disclination and the opticalleakage, that the second end portion of the first pixel electrode andthe fourth end portion of the third pixel electrode, that is, the endportions of the adjoining pixel electrodes at the identical polarity aredisposed on the flat face. This effect is remarkable especially when thedistance between the first pixel electrode and the third pixel electrodeis 2.0 μm or less (as referred to (2) “the ridges of the pixel electrodeend portions”).

[0058] In the present invention, moreover, the height of the first endportion and he third end portion are desired to be 0.5 μm or more withrespect to the main face of the pixel electrode. In other words, theheight of the first end portion and the third end portion is desired tobe 0.5 μm or closer to the opposed electrode with respect to the mainface of the pixel electrode. At this time, the width (L₁) of the firstend portion and the width (L₂) of the third end portion, as shown inFIG. 1A, have the optimum value, so that the effect to reduce thedisclination and the optical leakage cannot be obtained if the optimumvalue is exceeded. Unless the widths of the first end portion and thesecond end portion are suppressed within 3.0 μm from the end of thepixel electrode for the cell gap of 4.5 μm or less and for the distanceof 4.0 μm between the first pixel electrode and the second pixelelectrode, the sum of the widths for the optical leakage and thedisclination becomes larger than that of the case in which the first endportion and the third end portion are formed to have the same height asthat of the main face of the pixel electrode. This fact has beendescribed by using the graphs of FIG. 11 showing the relations betweenthe overlap width (i.e., the width of the first end portion) of thepixel electrode and the ridge and the sum of the widths for the opticalleakage and the disclination (as referred to (2) “the ridges of thepixel electrode end portions”).

[0059] In the sectional view of FIG. 4A showing the end portions of theadjoining pixel electrodes having the potentials of the differentpolarities, there are located the width (L₁) of the first end portion,the width (L₂) of the third end portion, the height of the first endportion and the height (h) of the third end portion. The first endportion 201 and the third end portion 203 rise with respect to the mainface of the pixel electrode and are located at a height close to theopposed electrode. In the sectional view of FIG. 4B showing the endportions of the adjoining pixel electrodes having the potentials of theidentical potential, it is shown that the second end portion 202 and thefourth end portion 204 are formed on the flat face.

[0060] In the liquid crystal display device for the source lineinversion drive, the positional relations of the end portions of thepixel electrode may be thought by replacing the first signal line 212Aof FIG. 2 and FIG. 1B by the first scanning line and the second signalline 212B by the second scanning line. Naturally, the first scanningline 207A is replaced by the first signal line, and the second scanningline 207B is replaced by the second signal line.

[0061] Specifically, according to the present invention, the liquidcrystal display device for the source line inversion drive ischaracterized: the pixel electrode includes the band-shaped first,second, third and fourth end portions and the main face surrounded bythese end portions; in that the main face is formed on the flat face; inthat there is further included the opposed electrode opposed to thepixel electrode; in that the first end portion is extended along thefirst signal line, the third end portion is extended along the secondsignal line adjoining the first signal line, the second end portion isextended along the first scanning line, and the fourth end portion isextended along the second scanning line adjoining the first scanningline; in that the first end portion and the third end portion areextended at their two end portions along the first scanning line and thesecond scanning line; in that the first end portion and the third endportion are nearly as high as the opposed electrode with respect to theflat face; and in that the second end portion and the fourth end portionare at the same height as that of the flat face.

[0062] Moreover, the liquid crystal display device is characterized: inthat the pixel electrode includes the first pixel electrode and thesecond pixel electrode adjoining the former in the row direction; and inthat the first end portion of the first pixel electrode and the thirdend portion of the second pixel electrode adjoin each other.

[0063] Moreover, the liquid crystal display device is characterized: inthat the first end portion and the third end portion are disposed at aheight of 0.5 μm or closer to the opposed electrode; and in that thewidth of the first end portion and the width of the third end portionare 3.0 μm or less from the end of the pixel electrode, when the liquidcrystal display device has a cell gap of 4.5 μm or less and when thedistance between the first pixel electrode and the second pixelelectrode is 4.0 μm or less.

[0064] In the ordinary liquid crystal display device of the activematrix type, the pixel electrode is mostly formed over the scanninglines and the signal lines. Therefore, the end portions of the pixelelectrode are necessarily formed mostly to rise with respect to the mainface of the pixel electrode to a height close to the opposed electrode.However, the effect to reduce the disclination and the optical leakageis not obtained merely by raising the end portions of the pixelelectrode with respect to the main face of the pixel electrode. It isassumed, for example, that the portions of the end portions of the pixelelectrode over a scanning line 3005 and the (not-shown) signal line risewith respect to the main face of the pixel electrode, as shown in aperspective view of the pixel electrodes arranged in a matrix shape inFIG. 31A. With this simple construction, the disclination and theoptical leakage, as caused generally in parallel with the scanning line3005 when in the gate line inversion drive, for example, are suppressedbecause the end portions of the pixel electrodes rise with respect tothe main face of the pixel electrodes. However, the end portion 3010 ofa pixel electrode 3006 and the end portion of a pixel electrode 3008, asadjoining each other in the identical polarity, rise with respect to themain face of the pixel electrodes so that the disclination and theoptical leakage will occur in parallel with the signal line of the pixelelectrodes.

[0065] When the pixel TFTs to be connected with the pixel electrodes areto be constructed, the end portions of the pixel electrodes may belocally raised by the thicknesses of the storage capacities and thesemiconductor layers connected in series with the pixel TFTs, as shownin the perspective view of the pixel electrodes arranged in the matrixshape in FIG. 31B. However, the mere rises of the end portions of thepixel electrodes, as locally caused merely by the thicknesses of thestorage capacities with respect to the main face of the pixelelectrodes, could not attain the effect to reduce the disclination andthe optical leakage. In the liquid crystal display device for the sourceline inversion drive, for example, it is nonsense to raise the endportions of the pixel electrodes along the scanning line 3005 withrespect to the main face of the pixel electrodes. Specifically, independence upon the gate line inversion drive or the source lineinversion drive of the liquid crystal display device, it is necessary toselect whether the portions rising from the main face of the pixelelectrode, such as the first end portion and the third end portion, areto be formed along the scanning line or the signal line. As shown in thetop plan view of the pixel electrodes of FIG. 1A, especially, the twoend portions 206A and 206B of the first end portion 201 and the two endportions 205A and 205B of the third end portion of the pixel electrode,as contacting with the pixel electrode of the different polarity andhaving the easily curving equipotential lines, have to be raised withrespect to the main face of the pixel electrode to a height close to theopposed electrode. The construction of the perspective view of FIG. 31Bcannot suppress the optical leakage and the disclination, as mightotherwise occur at the end portion 3012 of the pixel electrode.

[0066] In short, the construction of the pixel portion of the presentinvention has the structure, which has been decided by considering thepotentials of the adjoining pixel electrodes and the equipotential linescaused by the structure of the pixel electrodes, but is not absolutelydifferent from the structure which is necessarily made. Moreover, thestructure is obtained by examining how to establish the equipotentiallines systematically by the simulation so that it should be highlyappreciated in its effects, as compared with the method of the prior artfor reducing the disclination and the optical leakage.

[0067] In the simulation, as shown in FIG. 3, the section of the ridge304 below the first end portion and the third end portion of the pixelelectrode is formed into a rectangular shape. However, the presentinvention can also be applied to the simulation model of FIG. 3, inwhich the angle (as will be called the “taper angle of the ridge”), asmade between the side face of the ridge and the face contacting with themain face of the pixel electrode is 90 degrees or less. Where the taperangle of the ridge 304 is less than 90 degrees in the sectional view ofFIG. 5A showing the end portion of the pixel electrode, the abruptchange in the electric field in the vicinity of the crests of the ridgecan be suppressed, as compared with the structure in which the ridge hasthe rectangular section. Then, the electric field abruptly changes atthe crests of the rectangular ridge, as resulted by the simulation ofFIG. 15B, so that the phenomenon of the locally high transmittance canbe preferably prevented. Similar discussions apply to the case in whichthe section of the ridge is curved, as shown in the top plan view of theend portions of the pixel electrode in FIG. 5B. Thus, even when thesection of the ridge below the first end portion and the third endportion of the pixel electrode is not rectangular, on the contrary, itis predicted that the optical leakage and the disclination are notincreased by the first end portion and the third end portion, if thewidth (L₁) of the first end portion and the width (L₂) of the third endportion of the pixel electrode are suppressed within 3.0 μm, when thefirst end portion and the third end portion have a height (h) of 0.5 μmor more, when the cell gap is 4.5 μm or less and when the distance (s)between the pixel electrodes is 4.0 μm or less. Here, the width (L1) ofthe first end portion and the width (L₂) of the third end portion areapplied to the portions of the pixel electrode, which rise locally withrespect to the main face of the pixel electrode.

[0068] Construction 2 of Pixel Portion of the Invention

[0069] Here will be described the construction of the pixel portion ofthe present invention. A comparison is made between the simulationresults having examined how the optical leakage and the disclinationoccurred depending upon whether the adjoining pixel electrodes of FIG.13 to FIG. 16 have the potentials of the identical or differentpolarities. It is thought better that the height of the end portions ofthe pixel electrode is locally increased where the equipotential linesmake large curvatures, so as to suppress the curvatures of theequipotential lines of the pixel electrode end portions.

[0070] However, how much the end portions of the pixel electrode are tobe raised with respect to the main face of the pixel electrode has to bedetermined on the basis of the curving degree of the equipotential linesformed by the pixel electrodes adjoining each other. This could beunderstood by comparing the simulation results of FIG. 13 to FIG. 16.Specifically, if the heights of the end portions of the pixel electrodeare carelessly increased nearly to that of the opposed electrode evenwith little curvature of the equipotential lines, this determinationwill increase the disclination and the optical leakage (FIG. 15 and FIG.16). When the equipotential lines prominently curve at the end portionsof the pixel electrode, however, the end portions of the pixel electrodeare raised with respect to the main face of the pixel electrode to aheight close to the opposed electrode (FIG. 13 and FIG. 14).

[0071] If this concept is developed, moreover, the heights of the endportions of the pixel electrode may be made the larger for the moreintense curvatures of the equipotential lines at the end portions of thepixel electrode. In short, it is effective for preventing the opticalleakage and the disclination to determine the heights of the endportions of the pixel electrode in accordance with the curving degree ofthe equipotential lines.

[0072] The description will be made with reference to the top plan viewof the pixel electrode of FIG. 6A. In the case of a rectangular pixelelectrode 258, the intense curvatures of the equipotential lines arespecified to occur at the vicinities 255A and 255B, and 256A and 256B tothe crests of the pixel electrode. At these vicinities 255A and 255B,and 256A and 256B of the crests of the pixel electrodes close to the twopixel electrodes having the potentials of the different polarities,these equipotential lines are intensely curved by the influences of thepixel electrodes having the potentials of the different polarities. Inthe rectangular pixel electrodes, the vicinities of the crests of thepixel electrode, e.g., the two end portions 256A and 256B of a first endportion 251 may be raised with respect to the central portion 263 of thefirst end portion 251 of the pixel electrode. Moreover, the two endportions 255A and 255B of a third end portion 253 of the pixel electrodeare locally raised with respect to the central portion of the third endportion 253. Here, the central portion of the first end portion islocated at a position bisecting a segment which is formed of two points:one point (A) on the end of the pixel electrode, as contained in the twoend portions 256A of the first end portion; and an intersection point(B) between the straight line extending from that point (A) in parallelwith the row direction of the pixels and the other of the two endportions 256B of the first end portion. The central portion of the thirdend portion can be defined if the description thus far made is changedfrom the first end portion to the third end portion.

[0073] The characteristics of the pixel electrode of the presentinvention will be described with reference to the top plan view of thepixel portion of FIG. 7, in which the pixel electrodes are arranged inthe matrix shape. The first to fourth pixel electrodes 258 to 261 areshown in a matrix of 2×2. For the gate line inversion drive, the pixelelectrodes having the potentials of polarities different from that ofthe first pixel electrode 258 are the second pixel electrode 259 and thefourth pixel electrode 261. Specifically, one 256A of the two endportions 256A and 256B of the first end portion 251 of the first pixelelectrode adjoins the second pixel electrode 259 and the fourth pixelelectrode 261 having the potentials of the polarity different from thatof the first pixel electrode. Then, the equipotential lines areintensely curved at the two end portions 256A of the first end portionof the first pixel electrode by the influences of the electric fieldwhich is established by the second pixel electrode and the fourth pixelelectrode and by the two end portions 256A of the first end portion ofthe first pixel electrode.

[0074] Of the first to fourth pixel electrodes shown in the top planview of FIG. 7, therefore, the portions close to the two pixelelectrodes having the polarities of the different polarities, such asthe two end portions 256A and 256B of the first end portion and the twoend portions 255A and 255B of the third end portion are desired to belocally raised. Specifically, if the heights of the end portions of thepixel electrode are determined according to the curving degree of theequipotential lines at the pixel electrode end portions, the two endportions of the first end portion and the two end portions of the thirdend portion have large curvatures of the equipotential lines so thatthey necessarily have to be raised with respect to the main face of thepixel electrode. In other words, it is necessary to set the two endportions of the first end portion and the two end portions of the thirdend portion at positions close to the opposed electrode.

[0075] For example, the liquid crystal display device for the gate lineinversion drive may be given a structure in which the two end portionsof the first end portion and the third end portion, as located close tothe scanning line 263, of the end portions of the pixel electrode arelocally raised, as shown in the perspective view of FIG. 6B showing thepixel electrodes arranged in the matrix shape.

[0076] With reference to FIG. 7, the liquid crystal display device forthe gate line inversion drive according to the present invention isconstructed such that the pixel electrode includes the band shaped firstend portion 251, second end portion 252, third end portion 253 andfourth end portion 254, and the main face enclosed by those endportions. This main face is formed over the flat face and has theopposed electrode opposed to the pixel electrode. Moreover, the firstend portion is extended along the first scanning line 257A; the thirdend portion is extended along a second scanning line 257B adjoining thefirst scanning line; the second end portion is extended along a firstsignal line 262A; and the fourth end portion is extended along a secondsignal line 262B adjoining the first signal line. The two end portions255A and 255B, and 256A and 256B of the first end portion and the thirdend portion are extended along the first signal line and the secondsignal line. The first end portion and the third end portion aredisposed at a height close to the opposed electrode with respect to theflat face, and the second end portion and the fourth end portion aredisposed at the height equal to that of the flat face.

[0077] In this liquid crystal display device, moreover, the presentinvention is characterized in that the two end portions of the first endportion are disposed at a height closer to the opposed electrode thanthe central portion of the first end portion, and in that the two endportions of the third end portion are disposed at a height closer to theopposed electrode than the central portion of the third end portion.

[0078] Specifically, the present invention is characterized in that thetwo end portions of the first end portion are disposed at a heightcloser by a significant different of 0.2 μm or closer to the opposedelectrode than the central portion of the first end portion, and in thatthe two end portions of the third end portion are disposed at a heightcloser by 0.2 μm or closer to the opposed electrode than the centralportion of the third end portion.

[0079] Alternatively, the present invention is characterized in that thetwo end portions of the first end portion are disposed at a heightcloser by a significant different of 0.5 μm or closer to the opposedelectrode than the central portion of the first end portion, and in thatthe two end portions of the third end portion are disposed at a heightcloser by 0.5 μm or closer to the opposed electrode than the centralportion of the third end portion.

[0080] If the pixel electrode rises into a ridge shape by 0.2 μm ormore, or 0.5 μm or more, there is a significant effect to change how theequipotential lines are established to change the orientation of theliquid crystal, as seen from the graphs showing the results of thesimulation as shown in FIG. 11.

[0081]FIGS. 8A and 8B present the sectional views of the pixelelectrode, as taken along chain lines C-C′ and D-D′ from the top planview of FIG. 7. In FIG. 8B, there are defined the height (h1) of thefirst end portion and the third end portion of the pixel electrode 261,and the width (L₁) of the first end portion. Here, the fact that thefirst end portion has the height h1, namely, that the distance betweenthe face contacting with the main face of the pixel electrode and theuppermost end portion of the first end portion is h1 will mean that thefirst end portion of the pixel electrode is at a height close by h1 tothe opposed electrode. As shown in FIG. 8A, the two end portions of thefirst end portion of the pixel electrode 259 are raised to a height h2with respect to the central portion of the first end portion. Here, thefact that the distance between the face contacting with the centralportion of the first end portion and the uppermost end portion of thetwo end portions of the first end portion is h2 will mean that the twoend portions of the first end portion are disposed at a height closer byh2 to the opposed electrode than the central portion.

[0082] In the liquid crystal display device for the source lineinversion drive, it is sufficient to replace the scanning lines by thesignal lines and the signal lines by the scanning lines.

Example of Application Range of the Invention

[0083] The structure of the pixel portion thus made according to thepresent invention is that the lines of electric power when the electricfield is applied are normal to the formed flat face of the pixelelectrode, so that it can be widely used as means for reducing theorientation failure of the liquid crystal for both the orientationsystems of the normally white mode and the normally black mode.

[0084] If the orientation of the liquid crystal is not induced by thecorrugations, moreover, the present invention can be applied to theorientation system using the smectic liquid crystal. For example, thepresent invention can be applied to the liquid crystal display deviceusing a ferro-electric liquid crystal or an anti-ferro-electric liquidcrystal. Moreover, the present invention can also be applied to theliquid crystal display device using the material which has been set byadding a liquid polymer to the smectic liquid crystal and by irradiatingit with a beam (e.g., an ultraviolet ray).

[0085] The construction of the pixel portion of the present inventioncan be widely used as the means for adjusting the electric fielddistribution in the display device in which the optical modulation layeris optically modulated by applying a voltage thereto by a semiconductorelement.

[0086] Especially in the projection type liquid crystal display device,the optical leakage and the disclination are enlarged by the opticalsystem using lenses and are projected on the screen. Therefore, thepresent invention is effective especially in the projection type liquidcrystal display device.

[0087] The first end portion, the second end portion, the third endportion and the fourth end portion of the present invention need not berectangular, as shown in the top plan views. These end portions may befreely designed on the basis of the concept in which the portions of theequipotential lines to curve intensely at the time of driving the liquidcrystal display device are raised at the end portions of the pixelelectrode than the main face of the pixel electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0088]FIGS. 1A and 1B are a top plan view and a perspective view showinga pixel portion of the present invention;

[0089]FIG. 2 is a top plan view showing the pixel portion of the presentinvention;

[0090]FIG. 3 is a sectional view showing a model of a simulation;

[0091]FIGS. 4A and 4B are sectional views showing the pixel portion ofthe present invention;

[0092]FIGS. 5A and 5B are sectional views showing the pixel portion ofthe present invention;

[0093]FIGS. 6A and 6B are a top plan view and a perspective view showinga pixel portion of the present invention;

[0094]FIG. 7 is a top plan view showing the pixel portion of the presentinvention;

[0095]FIGS. 8A and 8B are sectional views showing the pixel portion ofthe present invention;

[0096]FIG. 9 is a top plan view showing one example of the pixel portionof the present invention;

[0097]FIG. 10 is a top plan view showing one example of the pixelportion of the present invention;

[0098]FIGS. 11A and 11B are diagrams plotting relations between thewidth of a first end portion and the sum of an optical leakage and thewidth of a disclination;

[0099]FIG. 12 is a schematic diagram showing a principle in which theoptical leakage and the disclination occur;

[0100]FIGS. 13A and 13B are sectional views showing the simulationresults in which the adjoining pixel electrodes are at potentials ofdifferent polarities;

[0101]FIG. 14 is a sectional view showing the simulation results inwhich the adjoining pixel electrodes are at potentials of differentpolarities;

[0102]FIGS. 15A and 15B are sectional views showing the simulationresults in which the adjoining pixel electrodes are at potentials of anidentical polarity;

[0103]FIG. 16 is a sectional view showing the simulation results inwhich the adjoining pixel electrodes are at potentials of an identicalpolarity;

[0104]FIGS. 17A and 17B are sectional views showing the simulationresults in which the adjoining pixel electrodes are at potentials of anidentical polarity;

[0105]FIG. 18 is a sectional view showing the simulation results inwhich the adjoining pixel electrodes are at potentials of an identicalpolarity;

[0106]FIGS. 19A and 19B are top plan views showing a process formanufacturing an active matrix substrate;

[0107]FIGS. 20A and 120B are top plan views showing a process formanufacturing the active matrix substrate;

[0108]FIG. 21 is a top plan view showing a process for manufacturing theactive matrix substrate;

[0109]FIG. 22 is a top plan view showing one example of the pixelportion of the present invention;

[0110]FIG. 23 is a sectional view showing one example of the activematrix substrate of the present invention;

[0111]FIG. 24 is a sectional view showing a liquid crystal displaydevice;

[0112]FIGS. 25A to 25F are perspective views showing examples ofelectronic devices;

[0113]FIGS. 26A to 26D are perspective views showing examples of theelectronic devices;

[0114]FIGS. 27A to 27C are perspective views showing examples of theelectronic devices;

[0115]FIGS. 28A and 28B are schematic diagrams showing equipotentiallines in which the adjoining pixel electrodes are at potentials of anidentical polarity;

[0116]FIGS. 29A to 29C are schematic diagrams showing equipotentiallines in which the adjoining pixel electrodes are at potentials ofdifferent polarities;

[0117]FIGS. 30A and 30B are diagrams showing the polarities of thevoltage to be applied to the pixels at the time for a source lineinversion drive; and

[0118]FIGS. 31A and 31B are perspective views showing examples to becompared with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] In order to retain the aperture ratio of the pixel portion of theliquid crystal display device, it is a recommended method to form theend portions of the pixel electrodes over the scanning lines, the signallines and the capacity electrodes by forming interlayer films over thescanning lines, the signal lines and the capacity electrodes. In the topplan views showing the embodiments of the present invention, however,the scanning lines, the signal lines and the pixel electrodes areconsciously shown distantly so that the positional relations between thecharacteristic portions of the pixel electrodes and the scanning linesand the signal lines may be easily understood. The method ofmanufacturing the recommendable liquid crystal display device will bedescribed in detail in connection with the embodiments.

[0120] In the liquid crystal display device for the source lineinversion drive, as shown in a top plan view of FIG. 9, a first endportion 201 of a first pixel electrode 208 and a third end portion 203of a second pixel electrode 209, as opposed to each other across asignal line 206, are raised with respect to the main face of the pixelelectrodes.

[0121] When the adjoining pixel electrodes are at the potentials of thedifferent polarities, the equipotential lines easily curve at the endportions of the adjoining pixel electrodes. Specifically, theequipotential lines easily curve between the first pixel electrode 208and the second pixel electrode 209. Therefore, it is recommended thatthe first end portion 201 and the third end portion 203 of the pixelelectrodes having the easily curving equipotential lines are raised withrespect to the main face of the pixel electrodes.

[0122] In case the first pixel electrode 208 and a third pixel electrode210 are at the potentials of an identical polarity, the equipotentiallines make a curvature in the gap between the first pixel electrode 208and the third pixel electrode 210, which is not considerably large inthe gap between the pixel electrodes of the identical potential. Whenthe first pixel electrode 208 and the third pixel electrode 210 adjoineach other, therefore, it is recommended that the second end portion andthe fourth end portion of the pixel electrode positioned across the gapare formed at the same level as that of the main face of the pixelelectrodes.

[0123] In FIG. 10, the pixel electrodes are formed into a polygonalshape having crests equal to or more than four. It is assumed that thedrive is the gate line inversion drive. In the liquid crystal displaydevice having a small pixel size, it is advantageous for writing thecharges in the storage capacity to perform the gate line inversiondrive.

[0124] A first end portion 251 and a third end portion 253 of a firstpixel electrode 258 and a second pixel electrode 259, as opposed eachother across a scanning line 257, are raised with respect to the mainface of the pixel electrodes. Moreover, the two end portions 256A and256B of the first end portion and the two end portions 255A and 255B ofthe third end portion are raised from the central portion of the firstend portion and the central portion of the third end portion withrespect to the main faces of the pixel electrodes so that the curvaturesof the equipotential lines may be corrected in the serious curvatureregion of the equipotential lines. The second end portion and the fourthend portion of the pixel electrodes are at the same level of that of themain faces of the pixel electrodes.

[0125] Below the first end portion and the third end portion, it isrecommended to pattern and form a photosensitive organic resin film andan organic resin film by a photolithography process. It is naturallypossible to pattern and form an inorganic film such as a silicon oxidefilm, a silicon nitride film or a silicon oxynitride film, too.

[0126] In order to make the two end portions of the first end portionlocally higher than the central portion of the first end portion, it isrecommended to form the photosensitive resin film separately twice. Itis also recommended to form the semiconductor layer, the scanning lines,and the signal lines and so on of the element substrate at the two endportions of the first end portion thereby to form the raised regionsselectively with respect to the main face of the pixel electrodes.

[0127] Embodiment 1

[0128] Embodiments of the present invention will now be described withreference to FIGS. 19 to 23.

[0129] First, an electrically conducting film is formed on a substrate601 having an insulating surface shown in a sectional view of FIG. 23B,and is patterned to form a scanning line 602. The scanning line alsoworks as a light-shielding film for protecting a semiconductor layerfrom light that will be formed later. Here, a quartz substrate is usedas a substrate 601, and a laminated-layer structure of a polysiliconfilm (50 nm thick) and a tungsten silicide (W-Si) film (100 nm thick) isused as the scanning line 602. Further, the polysilicon film preventsthe substrate from being contaminated with the tungsten silicide.

[0130] Next, an insulating film 603 is formed maintaining a thickness of100 to 1000 nm (typically, 300 to 500 nm) to cover the scanning line602. Here, a silicon oxide film having a thickness of 100 nm formed bythe CVD method and a silicon oxide film having a thickness of 280 nmformed by the LPCVD method are laminated one upon the other.

[0131] Then, an amorphous semiconductor film is formed maintaining athickness of 10 to 100 nm. Here, the amorphous silicon film is formedmaintaining a thickness of 69 nm by the LPCVD method. Next, theamorphous silicon film is crystallized by a technology disclosed inJapanese Patent Laid-Open No. 8-78329. According to the technologydisclosed in this publication, a metal element is selectively added tothe amorphous silicon film to promote the crystallization followed bythe heat treatment to form a crystalline silicon film which spreadsstarting from the region where the metal element is added. Here, nickelis used as a metal element for promoting the crystallization and, then,a heat treatment (450° C., one hour) is executed for dehydrogenation,followed by another heat treatment (600° C., 12 hours) forcrystallization.

[0132] Then, Ni is put to the gettering from the region where the activelayer of TFT is formed. The region of the active layer of TFT is coveredwith a mask (silicon oxide film), phosphorus (P) is added to a portionof the crystalline silicon film and is heat-treated (at 600° C. in anitrogen atmosphere for 12 hours).

[0133] Then, after the mask is removed, unnecessary portions of thecrystalline silicon film are removed by patterning to form semiconductorlayers 604 a and 604 b. The semiconductor layers 604 a and 604 b are thesame semiconductor layers 604. FIG. 19A is a top view of the pixel afterthe semiconductor layer is formed. There are shown a scanning line 602and a semiconductor layer 604.

[0134] Next, to form a storage capacity, a resist is formed, and aportion (region for forming the storage capacity) 604 b of thesemiconductor layer is doped with phosphorus.

[0135] Then, the resist is removed and an insulating film is formed tocover the semiconductor layer. Then, to increase the capacity of thestorage capacitor, a resist is formed, and the insulating film isremoved from the region 604 b where the storage capacity is to beformed.

[0136] Then, an insulating film (gate insulating film 605) is formed bythe thermal oxidation. Due to this thermal oxidation, thegate-insulating film finally acquires a thickness of 80 nm. On theregion where the storage capacity is to be formed, there is formed aninsulating film having a thickness smaller than that of other regions.It is desired that the insulating film has a thickness of 40 to 50 nm onthe region where the storage capacity is to be formed.

[0137] Next, the channel doping is effected onto the whole surface orselectively to add p-type or n-type impurities at a low concentration tothe region that serves as the channel region of the TFT. The step ofthis channel doping is the one for controlling the threshold voltage ofthe TFT. Here, boron is added by the ion-doping method by excitingdiborane (B₂H₆) by plasma but without effecting the mass separation. Itis, of course, allowable to employ the ion plantation method byeffecting the mass separation.

[0138] Next, contact holes that reach the scanning lines are formed byetching the insulating film.

[0139] Then, an electrically conducting film is formed and is patternedto form a gate electrode 606 a and a capacitor wiring 606 b. Here, useis made of a laminated-layer structure of a silicon film (150 nm thick)doped with phosphorus and a tungsten silicide film (150 nm thick). Thestorage capacitor is formed by parts of the capacitor wiring and of thesemiconductor layer with the insulating film 605 as a dielectric.

[0140]FIG. 19B is a top view of a pixel after the gate electrode and thecapacitor wiring are formed. The gate electrode 606 a is electricallyconductive to the scanning line 602 through a contact hole 801. A regionwhere the semiconductor layer 604 is overlapped on the capacitor wiring606 b via an insulating film works as the storage capacitor.

[0141] Then, by using the gate electrode and the capacitor wiring asmasks, phosphorus is added at a low concentration in a self-alignedmanner. The concentration of phosphorus in the region to where it isadded at a low concentration, is adjusted to be from 1×10¹⁶ to 5×10¹⁸atoms/cm³ and, typically, from 1×10¹⁶ to 5×10¹⁸ atoms/cm³.

[0142] Next, a resist is formed and phosphorus is added at a highconcentration by using the resist as a mask, thereby to form a regioncontaining impurities at a high concentration that serves as a sourceregion or a drain region. The phosphorus concentration in the region ofthe high impurity concentration is adjusted to be from 1×10₂₀ to 1×10²¹atoms/cm³ and, typically, from 2×10²⁰ to 5×10₂₀ atoms/cm³. In thesemiconductor layer, a region overlapped on the gate electrode serves asa channel region, and a region covered with a resist serves as animpurity region of a low concentration and works as an LDD region. Afterthe impurities are added, the resist is removed.

[0143] Though not diagramed, the region that becomes an n-channel TFT iscovered with a resist, and boron is added to form a source region or adrain region in order to form a p-channel TFT used for a driver circuitformed on the same substrate as the pixels.

[0144] Next, after the resist is removed, a passivation film 607 isformed to cover the gate electrode 606 a and the capacitor wiring 606 b.Here, a silicon oxide film is formed maintaining a thickness of 70 nm.Next, the heat treatment is effected to activate the n-type or p-typeimpurities added into the semiconductor layer at their respectiveconcentration. Here, the heat treatment is effected at 950° C. for 30minutes.

[0145] Then, an interlayer insulating film 608 of an inorganic materialis formed. In this Embodiment, a silicon oxynitride film is formedmaintaining a thickness of 800 nm.

[0146] Then, a contact hole is formed to reach the semiconductor layer,and an electrode 610 and a signal line 609 are formed. In thisEmbodiment, the electrode and the signal lines are formed of alaminated-layer film of a four-layer structure in which a Ti film isformed maintaining a thickness of 60 nm, a TiN film is formedmaintaining a thickness of 40 nm, an aluminum film containing Si isformed maintaining a thickness of 300 nm, and a TiN film is formedmaintaining a thickness of 100 nm all by sputtering in a continuousmanner.

[0147]FIG. 20A is a top view of the pixel after the electrode and thesignal lines are formed. The signal line 609 is electrically conductiveto the semiconductor layer through the contact hole 802. The electrode803 is electrically conductive to the semiconductor layer through thecontact hole 803.

[0148] Then, the hydrogenation treatment is effected at 350° C. for onehour.

[0149] Next, an interlayer insulating film 612 of an organic resinmaterial is formed. An acrylic resin film of 1.0 μm thickness is usedhere. Thereafter, a light-shielding electrically conducting film isformed maintaining a thickness of 100 nm on the interlayer-insulatingfilm to thereby form a light-shielding film 613.

[0150] Here, a top plan view of a pixel portion after a shielding film613 was formed is shown in FIG. 20B. The shielding film 613 has a roleto prevent the optical leakage and the disclination from being visuallyconfirmed, and a role to shield the electric field, as established as aresult that the signal line has a potential, so that the orientation ofthe liquid crystal may not be disturbed by the potential owned by thesignal line. For this, the shielding layer overlaps a signal line 609.

[0151] The shielding film 613 over the signal line 609 is formed in thegap between the pixel electrode and the pixel electrode, as will bedescribed hereinafter. As a result, the corrugations due to the filmthickness of the shielding film are not formed at the end portions ofthe pixel electrodes along the signal line. The end portions of a pixelelectrode 616 along the signal line are formed on a flat face.

[0152] Next, an insulating film 614 is formed to have a thickness of 100nm. This insulating film forms a silicon oxynitride film having athickness of 100 nm to 300 nm.

[0153] Next, a photosensitive resin film is used to perform aphotolithography step thereby to form a ridge 615 of a thickness of 0.5μm along the scanning line. The photosensitive resin film uses amaterial which lowers the viscosity by diluting BPR-107VL of JSR Companywith PGMEA (Propylene Glycol Monomethyl Ether Acetate).

[0154] Next, contact holes are formed to reach the electrodes. Next, atransparent conductive film (e.g., an indium-tin oxide (ITO) film) of100 nm is formed and is patterned to form the pixel electrodes 616.

[0155] Here, there can be formed a storage capacitor 617 by making thepixel electrodes and the shielding film 613 into the electrodes and theinsulating film 614 into a dielectric member.

[0156] Here, the top plan view of the pixels after the pixel electrodes616 were formed is shown in FIG. 21. An electrode 610 and the pixelelectrode are conducted through a contact hole 804. The ridge 615, asformed along the scanning line, has a pattern of a slender square. Thedistance (s) between the pixel electrode and the pixel electrode is 2.0μm, and the overlap width (L) between the pixel electrode and the ridgeis 1.0 μm.

[0157] The substrate thus manufactured by the steps thus far describedwill be called the “active matrix substrate”.

[0158] The top plan view showing the electrodes, the wiring lines andthe semiconductor layer formed in the pixel portion are presented inFIG. 22. A section, as cut along chain lines E-E′ and F-F′ from the topplan view of FIG. 22, is present in FIG. 23.

[0159] The present embodiment is only one example, and it is needless tosay that the present invention should not be limited to the steps of thepresent embodiment. For example, each conductive film may be exemplifiedby one made of tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), chromium (Cr) or silicon (Si).

[0160] The active matrix substrate of the present embodiment can be usedin a transmission type liquid crystal display device. When a conductivefilm having a function to reflect a light is used as a pixel electrodein place of the transparent conductive film, the active matrix substrateof the present embodiment can be used in a reflection liquid crystaldisplay device.

[0161] Embodiment 2

[0162] This embodiment deals with the steps for fabricating a liquidcrystal display device of the active matrix type using the active matrixsubstrate fabricated in Embodiment 1. The description refers to FIG. 24.

[0163] First, the active matrix substrate is obtained in accordance withEmbodiment 1.

[0164] Next, a transparent electrode 701 of a transparent electricallyconducting film is formed on a light-transmitting substrate 700. In thisembodiment, the thus constituted substrate is called opposing substrate.

[0165] Then, an oriented film 703 is formed on the active matrixsubstrate and on the opposing substrate, and is rubbed. The liquidcrystal display device fabricated according to this Embodiment is apanel of the projection type having a diagonal size of from about 0.3inches to about 1 inch. In the panel of this kind, the pixels have asize of as small as 10 μm to 20 μm, and the defect caused by spacersbecomes no longer negligible. The liquid crystal display device of thisembodiment, therefore, uses no spacer.

[0166] The active matrix substrate on which the pixel portions and thedriver circuits are formed, is stuck to the opposing substrate with asealing member. The sealing member contains a filler, and the two piecesof substrates are stuck together maintaining a uniform gap due to thefiller. The cell gap between the pixel portions is 4.5 μm.

[0167] Thereafter, a liquid crystal material 704 is poured into betweenthe two substrates, and is completely sealed with a sealing agent (notshown). The liquid crystal material 704 may be a known material. Thus,the liquid crystal display device of the active matrix type is completedas shown in FIG. 24. As required, further, the active matrix substrateor the opposing substrate is divided into a desired shape. Further, apolarizer plate is suitably provided relying upon the known technology.An FPC is stuck, too, according to the known technology.

[0168] Referring to Embodiment 1, the liquid crystal display device isformed that is constituted the following; the cell gap to be 4.5 μm, thedistance between the pixel electrodes is 2.0 μm, the height to be 0.5μm, and the widths (L) of overlapping portion with the pixel electrodeand the height to be 1.0 μm. It is estimated that the sum of widths bywhich the leakage of light and the disclination are decreased is 2.2 μmas compared with when there is no height by the graph of FIG. 11.

[0169] Thus fabricated liquid crystal display panel can be used as adisplay unit for a variety of electronic devices.

[0170] Embodiment 3

[0171] The liquid crystal display device formed by implementing anembodiment between above-mentioned Embodiments 1 and 2 can be applied tovarious electro-optical equipments. Thus the present invention can beapplied to all of the electronic equipments having these electro-opticaldevices as the display portion.

[0172] The following can be given as examples of the electronicequipment: video cameras; digital cameras; projectors; head mounteddisplays (goggle type display); car navigation systems; car stereo;personal computers; portable information terminals (such as mobilecomputers, portable telephones and electronic notebook). An example ofthese is shown in FIGS. 25, 26 and 27.

[0173]FIG. 25A shows a personal computer, and it includes a main body2001, an image input section 2002, a display portion 2003, and akeyboard 2004. The present invention is applicable to the displayportion 2003.

[0174]FIG. 25B shows a video camera, and it includes a main body 2101, adisplay portion 2102, a voice input section 2103, operation switches2104, a battery 2105, and an image receiving section 2106. The presentinvention is applicable to the display portion 2102.

[0175]FIG. 25C shows a mobile computer, and it includes a main body2201, a camera section 2202, an image receiving section 2203, operationswitches 2204, and a display portion 2205. The present invention isapplicable to the display portion 2205.

[0176]FIG. 25D shows a goggle type display, and it includes a main body2301; a display portion 2302; and an arm section 2303. The presentinvention is applicable to the display portion 2302.

[0177]FIG. 25E shows a player using a recording medium which records aprogram (hereinafter referred to as a recording medium), and it includesa main body 2401; a display portion 2402; a speaker section 2403; arecording medium 2404; and operation switches 2405. This player uses DVD(digital versatile disc), CD, etc. for the recording medium, and can beused for music appreciation, film appreciation, games and Internet. Thepresent invention is applicable to the display portion 2402.

[0178]FIG. 25F shows a digital camera, and it includes a main body 2501;a display portion 2502; a view finder 2503; operation switches 2504; andan image receiving section (not shown in the figure). The presentinvention can be applied to the display portion 2502.

[0179]FIG. 26A is a front-type projector, and it includes a projectiondevice 2601 and a screen 2602. The present invention is applicable to aliquid crystal display device 2808 which comprises one of the projectiondevice 2601.

[0180]FIG. 26B is a rear-type projector, and it includes a main body2701, a projection device 2702, a mirror 2703, and a screen 2704. Thepresent invention is applicable to a liquid crystal display device 2808which comprises one of the projection device 2702.

[0181]FIG. 26C is a diagram showing an example of the structure of theprojection devices 2601, 2702 in FIGS. 26A and 26B. The projectiondevice 2601 or 2702 comprises a light source optical system 2801,mirrors 2802, 2804 to 2806, dichroic mirrors 2803, a prism 2807, liquidcrystal display devices 2808, phase difference plates 2809, and aprojection optical system 2810. The projection optical system 2810 iscomposed of an optical system including a projection lens. This exampleshows an example of three-plate type but not particularly limitedthereto. For instance, the invention may be applied also to a singleplate type optical system. Further, in the light path indicated by anarrow in FIG. 26C, an optical system such as an optical lens, a filmhaving a polarization function, a film for adjusting a phase difference,and an IR film may be suitably provided by a person who carries out theinvention.

[0182]FIG. 26D is a diagram showing an example of the structure of thelight source optical system 2801 in FIG. 26C. In this embodiment, thelight source optical system 2801 comprises a reflector 2811, a lightsource 2812, lens arrays 2813, 2814, a polarization conversion element2815, and a condenser lens 2816. The light source optical system shownin FIG. 26D is merely an example, and is not particularly limited to theillustrated structure. For example, a person who carries out theinvention is allowed to suitably add to the light source optical systeman optical system such as an optical lens, a film having a polarizationfunction, a film for adjusting a phase difference, and an IR film.

[0183] Note that a transmission electro-optical device is used as theprojector shown in FIG. 26, a reflection type electro-optical device isnot illustrated.

[0184]FIG. 27A is a portable telephone, and it includes a main body2901, an audio output section 2902, an audio input section 2903, adisplay portion 2904, operation switches 2905, and an antenna 2906. Thepresent invention can be applied to the display portion 2904.

[0185]FIG. 27B is a portable book (electronic book), and it includes amain body 3001, display portions 3002 and 3003, a recording medium 3004,operation switches 3005, and an antenna 3006. The present invention canbe applied to the display portions 3002 and 3003.

[0186]FIG. 27C is a display, and it includes a main body 3101, a supportstand 3102, and a display portion 3103. The present invention can beapplied to the display portion 3103. The display of the presentinvention is advantageous for a large size screen in particular, and isadvantageous for a display equal to or greater than 10 inches(especially equal to or greater than 30 inches) in diagonal.

[0187] The applicable range of the present invention is thus extremelywide, and it is possible to apply the present invention to electronicequipment in all fields. Further, the electronic equipment of Embodiment3 can be realized by using a constitution of any combination ofEmbodiments 1 and 2.

[0188] As has been described hereinbefore, according to the presentinvention, the orientation failures of the liquid crystal such as thedisclination or optical leakage of the liquid crystal display devicewhen the black level is displayed can be reduced to provide a liquidcrystal display device which has a high contrast and an excellentvisibility.

[0189] When the adjoining pixel electrodes have the differentpolarities, as shown in a sectional view in FIG. 29, equipotential lines903 curve at the end portions of the pixel electrode 901 a and the pixelelectrode 901 b. The opposed electrode 902 is at 0 V (FIG. 29A). If thepixel electrodes 901 a and 901 b are provided below their first endportions with ridges 904, equipotential lines are formed along the pixelelectrodes so that their curvatures are suppressed at the end portionsof the pixel electrodes (FIG. 29B). As the overlap widths 905 of thepixel electrodes and the ridges are enlarged, even the equipotentiallines intrinsically parallel to the pixel electrode faces will curve(FIG. 29C). Accordingly, the optical leakage and the disclinationincrease. When the adjoining pixel electrodes are different inpolarities, therefore, the ridges below the first end portions of thepixel electrodes are preferably formed to optimize the overlap widthsbetween the pixel electrodes and the ridges.

[0190] When the adjoining pixel electrodes have the identical polarity,as shown in a sectional view of FIG. 28, the equipotential lines 903curve at the end portions of the pixel electrode 901 a and the pixelelectrode 901 b, but the curving degrees are small (FIG. 28A).Therefore, the ridges 904 formed below the end portions of the pixelelectrodes will increase the curvatures of the equipotential lines tocause adverse effects (FIG. 28B).

[0191] The present invention makes use of this principle to prevent thecurvatures of the equipotential lines at the end portions of the pixelelectrodes thereby to increase the electric field normal to the surfaceof the opposed electrode and to reduce the disclination and the opticalleakage.

What is claimed is:
 1. A liquid crystal display device comprising: a scanning line over a substrate; a signal line intersecting the scanning line over the substrate; a pixel electrode electrically connected to the scanning line and the signal line over the substrate; and an opposed electrode over the pixel electrode, wherein the pixel electrode contains a main face, a first face closer to the opposed electrode than the main face, and a second face closer to the opposed electrode than the first face, wherein the first face is extended along the scanning line, and wherein the second face is adjacent to an intersection between the scanning line and the signal line.
 2. A liquid crystal display device according to claim 1, wherein the liquid crystal display device is driven by a gate line inversion drive.
 3. A liquid crystal display device according to claim 1, wherein the liquid crystal display device is incorporated in one selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a DVD player, a digital camera, a projector, a portable telephone, and a portable electronic book.
 4. A liquid crystal display device comprising: a plurality of pixel electrodes over a substrate, each of the plurality of pixel electrodes containing a main face, and first to fourth end portions enclosing the main face, wherein the first end portion is extended along a first scanning line, and the third end portion is extended along a second scanning line adjacent to the first scanning line, and wherein the second end portion is extended along a first signal line and interposed between the first end portion and the third end portion, and the fourth end portion is extended along a second signal line adjacent to the first signal line and interposed between the first end portion and the third end portion; and an opposed electrode over the plurality of pixel electrodes, wherein the second end portion and the fourth end portion are at a same height as the main face, and the first end portion and the third end portion are disposed closer to the opposed electrode than the main face, wherein two end portions of the first end portion are further closer to the opposed electrode than the center of the first end portion, and wherein two end portions of the third end portion are further closer to the opposed electrode than the center of the third end portion.
 5. A liquid crystal display device according to claim 4, wherein the liquid crystal display device is driven by a gate line inversion drive.
 7. A liquid crystal display device according to claim 4, wherein the plurality of pixel electrodes are adjacent to each other such that a distance between the second end portion of one pixel electrode and the fourth end portion of the other pixel electrode is 2.0 μm or less.
 8. A liquid crystal display device according to claim 4, wherein the two end portions of the first end portion are closer by 0.5 μm or more to the opposed electrode than the central portion of the first end portion.
 9. A liquid crystal display device according to claim 4, wherein the two end portions of the third end portion are closer by 0.5 μm or more to the opposed electrode than the central portion of the third end portion.
 10. A liquid crystal display device according to claim 4, wherein the liquid crystal display device is incorporated in one selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a DVD player, a digital camera, a projector, a portable telephone, and a portable electronic book.
 11. A liquid crystal display device comprising: a scanning line over a substrate; a signal line intersecting the scanning line over the substrate; a pixel electrode electrically connected to the scanning line and the signal line over the substrate; and an opposed electrode over the pixel electrode, wherein the pixel electrode contains a main face, a first face closer to the opposed electrode than the main face, and a second face closer to the opposed electrode than the first face, wherein the first face is extended along the signal line, and wherein the second face is adjacent to an intersection between the scanning line and the signal line.
 12. A liquid crystal display device according to claim 11, wherein the liquid crystal display device is driven by a source line inversion drive.
 13. A liquid crystal display device according to claim 11, wherein the liquid crystal display device is incorporated in one selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a DVD player, a digital camera, a projector, a portable telephone, and a portable electronic book.
 14. A liquid crystal display device comprising: a plurality of pixel electrodes over a substrate, each of the plurality of pixel electrodes containing a main face, and first to fourth end portions enclosing the main face, wherein the first end portion is extended along a first signal line, and the third end portion is extended along a second signal line adjacent to the first signal line, and wherein the second end portion is extended along a first scanning line and interposed between the first end portion and the third end portion, and the fourth end portion is extended along a second scanning line adjacent to the first scanning line and interposed between the first end portion and the third end portion; and an opposed electrode over the plurality of pixel electrodes, wherein the second end portion and the fourth end portion are at a same height as the main face, and the first end portion and the third end portion are disposed closer to the opposed electrode than the main face, wherein two end portions of the first end portion are further closer to the opposed electrode than the center of the first end portion, and wherein two end portions of the third end portion are further closer to the opposed electrode than the center of the third end portion.
 15. A liquid crystal display device according to claim 14, wherein the liquid crystal display device is driven by a source line inversion drive.
 16. A liquid crystal display device according to claim 14, wherein the plurality of pixel electrodes are adjacent to each other such that a distance between the second end portion of one pixel electrode and the fourth end portion of the other pixel electrode is 2.0 μm or less.
 17. A liquid crystal display device according to claim 14, wherein the two end portions of the first end portion are closer by 0.5 μm or more to the opposed electrode than the central portion of the first end portion.
 18. A liquid crystal display device according to claim 14, wherein the two end portions of the third end portion are closer by 0.5 μm or more to the opposed electrode than the central portion of the third end portion.
 19. A liquid crystal display device according to claim 14, wherein the liquid crystal display device is incorporated in one selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a DVD player, a digital camera, a projector, a portable telephone, and a portable electronic book.
 20. A liquid crystal display device comprising: a scanning line over a substrate; a signal line intersecting the scanning line over the substrate; a pixel electrode electrically connected to the scanning line and the signal line over the substrate; and an opposed electrode over the pixel electrode, wherein the pixel electrode contains a main face, and a first face closer to the opposed electrode than the main face, and wherein the first face is extended along the scanning line.
 21. A liquid crystal display device according to claim 20, wherein the liquid crystal display device is driven by a gate line inversion drive.
 22. A liquid crystal display device according to claim 20, wherein the liquid crystal display device is incorporated in one selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a DVD player, a digital camera, a projector, a portable telephone, and a portable electronic book.
 23. A liquid crystal display device comprising: a scanning line over a substrate; a signal line intersecting the scanning line over the substrate; a pixel electrode electrically connected to the scanning line and the signal line over the substrate; and an opposed electrode over the pixel electrode, wherein the pixel electrode contains a main face, and a first face closer to the opposed electrode than the main face, and wherein the first face is extended along the signal line.
 24. A liquid crystal display device according to claim 23, wherein the liquid crystal display device is driven by a source line inversion drive.
 25. A liquid crystal display device according to claim 23, wherein the liquid crystal display device is incorporated in one selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a DVD player, a digital camera, a projector, a portable telephone, and a portable electronic book. 